Nucleation-Mode-Particle Emissions from Biosolid Processing Plants

Although modern technologies have significantly reduced mass emissions of particulate matter, there remains growing concern about the number emissions of particles smaller than 10 nm in diameter. Despite their minimal contribution to total aerosol mass, these particles have high surface-to-volume ratios, making them highly reactive and capable of penetrating deep into the respiratory tract. Here we show that biosolid processing facilities can emit nanoparticles. Repeated and persistent episodes of elevated particle number concentrations (PNs) were observed downwind from a facility, frequently exceeding 200,000 cm^-3 for particles between 5 and 20 nm in mobility diameter. The PN correlated with elevated CO₂ levels used as a tracer for bacterial respiration. Emission factors ranged from 4.4 × 10¹⁴ to 3.7 × 10¹⁵ (kg CO₂)^-1. Transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy shows that particles were composed primarily of carbon, with some sulfur, nitrogen, and phosphorus. The observed agglomerated morphology suggests that the nucleation mode particles were either solid or highly viscous. The elevated number concentrations and morphology are consistent with particle formation via gas-phase nucleation, likely triggered by fugitive volatile organic compound emissions from the facility. Further research is needed to fully assess their impact on local air quality and public health.